The user space interface

Every registered input device is represented by a /dev/input/event<X> char device, from which we can read the event from the user space. An application reading this file will receive event packets in the struct input_event format:

struct input_event { 
  struct timeval time; 
  __u16 type; 
  __u16 code; 
  __s32 value; 
} 

Let's look at the meaning of each element in the structure:

• time is the timestamp. It returns the time at which the event happened.
• type is the event type; for example, EV_KEY for a key press or release, EV_REL for a relative moment, or EV_ABS for an absolute one. More types are defined in include/linux/input-event-codes.h.
• code is the event code; for example, REL_X or KEY_BACKSPACE. Again, a complete list is in include/linux/input-event-codes.h.
• value is the value that the event carries. For the EV_REL event type, it carries the relative change. For an EV_ABS (joysticks, and so on) event type, it contains the absolute new value. For the EV_KEY...